1. CSE350 Software Design and Engineering University of Pennsylvania http://www.cis.upenn.edu/~jms Office: 254 Moore GRW, Phone: 8-9509 April 2 nd, 2002

2. Administrative: Lectures lToday: Development methods wrap-up l4/9: Engineering Trustworthy Software l4/16: Wrap-up of semester (summary)

3. Classical Software Engineering lCarefully scoped out requirements lPerformed within a single organization lGoal: deliver a “software product” lMay use hierarchy (such as “Chief Programmer Teams” of Brooks) lSteps:%effort%life Design 33.3%3.3% Implement (Code) 16.7% 1.7% Test 50% 5% Deploy Maintain90%

4. Strengths of Classical Software Engineering lProcess resembles other engineered systems lCan apply formal methods: program correctness lCan make (very rough) resource estimates lClear interfaces to management; clear lines of responsibility lCan define many specialized models to achieve these steps: spiral, cleanroom, waterfall, etc. lConsiderable industrial experience, e.g. at pre-breakup AT&T

5. Weaknesses of Classical S.E. lCommunications cost avoidance (specialization + hierarchy) means best ideas may not come out lManagement often at fault for failed projects Managers either not chosen with technical expertise, or Chosen for technical expertise, not management Too slow to correct big errors lLike many industrial processes, workers may not be interested, motivated or competent In software, this really matters: most productive people are multiplicatively (5-100?) times more productive

6. Distributed Development with Open Source: Unix + Hackers + Networks lSource code allows deep understanding Read good code -> write good code Importantly, it allows tinkering luucp – Unix to Unix copy Powerful overlay of telephone network Used to architect the “USENET” / netnews: on- line communities lBSD variant of Unix funded by DARPA ARPAnet connectivity for Universities Good networking support BSD distribution under agnostic (non-GPL) terms

7. “Open Source” methodology lAvailable source code plus a common code base meant that modifications could be shared – just recompile lSubset of on-line community in addition to academics and foodies: hackers lNetworked hackers share all sorts of source code lBroadcast changes – the interested react lProgrammer skills differences exploited (top 5%?) lParallel debugging and testing (auditing) lAdd WWW to net, get a new O.S.: Linux

8. The Open Source Community at Present All working roughly the same problem Level of maturity is high Well established community Open source development model works - the “products” actually run and run well Security awareness in very high The base technology is relatively stable, but moldable (for now) Community is motivated by success Constraints of market share and ROI are secondary motivators (at best – love not money?)

9. Open Source is not a “silver bullet” “… As an experiment I also planted a comment which should raise eyebrows in some code I released years ago and which is fairly widely used just to see if I’d get any reaction from anyone (the comment says, in effect, ”Something really suspicious could happen here”, although that’s not the real text so you can’t just grep for it to find it :-). Noone has ever asked me about this, from which I assume that noone’s ever looked at the code they’re using. That’s kind of scary, because the comment isn’t in there just to annoy people, you really could build a rather nasty backdoor in there. There may actually be products out there which are released in binary-only form where the vendor has built in a backdoor at that point, although I saw a posting from foo@anon.org in alt.2600 saying he’d looked at the product and it was fine, so it must be OK.” – Peter Gutmann, on Peter Neumann’s “Robust Open Source” mail exploder

10. An interesting quandary regarding “Love vs. Money” lHow do programmers get paid? lShould companies produce open source software? lWhat about notions of “intellectual property” lShould software be an industry or should it just be an auxiliary activity to systems that use software? lWill there be a commercial marketplace?

11. A prediction (sure to be wrong!) lThere *is* a software marketplace lThe market is a distributed decision-making mechanism that uses price as a signalling technique lThe main role of open source software is to provide diversity and police commercial vendors into providing a better quality/$ product lMicrosoft is already doing this, with recent announcements by Bill Gates that “Security is Job #1”